Drug & supplement interaction

Arimistane + Letrozole

Letrozole brand name: Femara.

Moderate Interaction
Medically reviewed by · Updated February 2024
The bottom line Moderate

Arimistane has a moderate interaction with Letrozole. It is believed that Arimistane inhibits the aromatase enzyme, which may interact with other aromatase inhibitors.

Read the full interaction report
SeverityModerate
LikelihoodProbable
EvidenceC
What do Severity, Likelihood & Evidence mean?
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Interaction report

Arimistane and Letrozole

Here is the interaction we found between these two, with the evidence behind it.

Moderate

Aromatase Inhibitors

Why this applies to Letrozole

Letrozole falls under Aromatase Inhibitors — the group Arimistane interacts with.

It is believed that Arimistane inhibits the aromatase enzyme, which may interact with other aromatase inhibitors. This interaction could potentially increase the risk of side effects associated with low estrogen levels or from additive side effects, such as an increased risk of liver toxicity. It is recommended to consult with a healthcare provider before combining Arimistane with other aromatase inhibitors to assess the potential risks and benefits.
Severity Moderate Likelihood Probable Evidence C

Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the thing to know: both Arimistane and your letrozole (Femara) work the same way. They block aromatase, the enzyme that makes estrogen. So stacking them isn't adding a different drug, it's basically doubling down on the same job. That can push your estrogen even lower than your cancer treatment intends and pile on the same side effects.

With letrozole, that usually means more hot flashes, joint and bone aches, fatigue, and over time thinner bones. There's also a concern about added strain on the liver. Arimistane has very little safety data and isn't a true supplement, so I'd be cautious. Please don't change your letrozole, but do run this by your oncologist or pharmacist before adding Arimistane.

Contact Dr. Brian directly if you have additional questions on this interaction

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Arimistane Also Interacts With Other Medications

Arimistane has 3 moderate known drug interactions in our database — the Letrozole one above is one of them. If you take anything else, check it against the full list below.

Moderate 3 No known interaction 2,827 (incl. Letrozole)
Taking anything else?

Check Another of Your Medications Against Arimistane

Covers the 2,830 medications we’ve checked against Arimistane. Pick one to open its full report.

From our Q&A

Questions About Arimistane or Letrozole

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Arimistane or Letrozole, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Letrozole

This page covers Arimistane only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Letrozole page lists 142 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), St. John's Wort (major), 7-methoxyflavone (moderate) and Acacia Rigidula (moderate).

By severity: 3 major · 99 moderate · 40 minor.

From our pharmacist’s overview on the Letrozole page

“Letrozole (Femara) is prescribed to keep hormone-driven breast cancer from returning, so a supplement that shifts its blood level can quietly undercut treatment. Give this list of 142 ingredients genuine respect, and learn the three major entries first.”

Reviewed by 2 · Jul 18, 2026

Open the Letrozole interaction page

One more smart check

Taking Arimistane as Part of a Dietary Supplement Product? Check It for Interactions

We hold 80 real supplement products containing Arimistane, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Arimistane. Your product may carry other ingredients that interact with Letrozole too, on top of Arimistane — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Arimistane and Letrozole Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Arimistane
Top half

#393 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Letrozole
Top 5%

#64 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Arimistane

What is Arimistane?

Arimistane
  • Lowering estrogen levels
  • Post-cycle therapy after steroid or prohormone use
  • Reducing gynecomastia ('gyno')
  • Boosting testosterone
  • Bodybuilding and physique support

Arimistane (sometimes sold as Estrovade) is a synthetic aromatase inhibitor marketed as a dietary supplement to lower estrogen and raise testosterone, often during or after steroid or prohormone cycles. It is not a true dietary ingredient, has very little human safety data, and U.S. regulators have warned against products containing aromatase inhibitors. Talk to a pharmacist or doctor before using it.

Read the full Arimistane monograph & all interactions
Medication

About Letrozole

What Is Letrozole Used For?

Brand name: Femara

Letrozole (brand name Femara, or available as generic letrozole tablets) is used to treat breast cancer in postmenopausal women whose tumors are hormone receptor positive — meaning the cancer feeds on estrogen. It is used in several situations: as an adjuvant treatment (therapy given after primary treatment to reduce the risk of the cancer returning) for early breast cancer, and as extended adjuvant treatment for women who have already completed five years of tamoxifen therapy.

Femara and letrozole tablets are also used as first-line or second-line treatment for locally advanced or metastatic (spread to other areas) breast cancer in postmenopausal women, including cases where the cancer has progressed after other anti-estrogen therapy.

See full Letrozole drug information
Keep checking

Other Drugs & Arimistane

Browse every other medication we’ve checked against Arimistane — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
3Moderate
0Minor
2,826No known interaction
3 Moderate 2,826 No interaction
Moderate

3 interactions

No interaction 2,826 drugs checked — show the list

We also checked Arimistane against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,826 medications checked with no known interaction — see the full Arimistane list.

See the full Arimistane interactions page
See every supplement checked against Letrozole, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Arimistane monograph › Uses, safety, and every drug interaction in one place Letrozole supplement interactions › Every supplement checked against Letrozole, ranked by severity Letrozole drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Arimistane and Letrozole Together: Common Questions

Can you take Arimistane with Letrozole?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Arimistane and Letrozole interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Letrozole and Arimistane?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.